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Bài 1
a) \(5\times72\times10\times2=\left(5\times2\times10\right)\times72=100\times72=7200\)
b) \(40\times125=5\times\left(8\times125\right)=5\times1000=5000\)
c) \(16\times6\times25=4\times4\times6\times25=\left(4\times6\right)\times\left(4\times25\right)=24\times100=2400\) Bài 2:
a) \(24\times57+43\times24=24\times\left(57+43\right)=24\times100=2400\)
b) \(12\times19+80\times12+12=12\times\left(19+80+1\right)=12\times100=1200\)
c) \(\left(36\times15\times169\right)\div\left(5\times18\times13\right)\)
\(=\left(18\times2\times3\times5\times13\times13\right)\div\left(5\times18\times13\right)\)
\(=\left(2\times3\times13\right)\times\left(18\times5\times13\right)\div\left(5\times18\times13\right)\)
\(=2\times3\times13\)
\(=78\)
d) \(\left(44\times52\times60\right)\div\left(11\times13\times15\right)\)
\(=\left(4\times11\times4\times13\times4\times15\right)\div\left(11\times13\times15\right)\)
\(=\left(4\times4\times4\right)\times\left(11\times13\times15\right)\div\left(11\times13\times15\right)\)
\(=4\times4\times4\)
\(=64\)
Bài 3:
a) \(x-280\div35=5\times54\)
\(x-8=270\)
\(x=270+8\)
\(x=278\)
b) \(\left(x-280\right)\div35=54\div4\)
\(\left(x-280\right)\div35=\dfrac{27}{2}\)
\(x-280=\dfrac{27}{2}\times35\)
\(x-280=\dfrac{945}{2}\)
\(x=\dfrac{945}{2}+280\)
\(x=\dfrac{1505}{2}\)
c) \(\left(x-128+20\right)\div192=0\)
\(x-128+20=0\times192\)
\(x-128+20=0\)
\(x-128=0-20\)
\(x-128=-20\)
\(x=-20+128\)
\(x=108\)
d) \(4\times\left(x+200\right)=460+85\times4\)
\(4\times\left(x+200\right)=460+340\)
\(4\times\left(x+200\right)=800\)
\(x+200=800\div4\)
\(x+200=200\)
\(x=200-200\)
\(x=0\)
Bài 4:
a) \(\dfrac{7}{12}-\dfrac{5}{12}=\dfrac{2}{12}=\dfrac{1}{6}\)
b) \(\dfrac{8}{11}+\dfrac{19}{11}=\dfrac{27}{11}\)
c) \(\dfrac{3}{8}+\dfrac{5}{12}=\dfrac{9}{24}+\dfrac{10}{24}=\dfrac{19}{24}\)
d) \(\dfrac{3}{4}+\dfrac{7}{12}=\dfrac{9}{12}+\dfrac{7}{12}=\dfrac{16}{12}=\dfrac{4}{3}\)
Bài 5:
a) \(x-\dfrac{6}{7}=\dfrac{5}{2}\)
\(x=\dfrac{5}{2}+\dfrac{6}{7}\)
\(x=\dfrac{47}{14}\)
b) \(\dfrac{12}{7}\div x+\dfrac{2}{3}=\dfrac{7}{5}\)
\(\dfrac{12}{7}\div x=\dfrac{7}{5}-\dfrac{2}{3}\)
\(\dfrac{12}{7}\div x=\dfrac{11}{15}\)
\(x=\dfrac{12}{7}\div\dfrac{11}{15}\)
\(x=\dfrac{180}{77}\)
= (8x15x24x35x...x99) / (9x16x25x36x...x100)
= (4x2x5x3x6x2x2x5x7x...x9x11) / (9x4x2x2x5x5x6x3x2x...x25x4)
= 11/(4x25)
= 11/100
Mình không chắc lắm
24x5+12x8+36x15+12x17+24x10
=12x10+12x8+12x45+12x17+12x20
=12x(10+8+45+17+20)
=12x100=1200
24 x 5 + 12 x 8 + 36 x 15 + 12 x 17 + 24 x 10
= 24 x (5 + 10) + 12 x (8 + 17) + 36 x 15
= 24 x 15 + 12 x 25 + 36 x 15
= 12 x 30 + 12 x 25 + 12 x 45
= 12 x (30 + 25 + 45)
= 12 x 100
= 1200
a, (36+24) : 0,6 = 60 : 0,6 = 100
(36+24) : 0,6 = 36 : 0,6 + 24 : 0,6 = 60 + 40 = 100
b, (99-66) : 0,33 = 33 : 0,33 = 100
(99-66) : 0,33 = 99 : 0,33 - 66 : 0,33 = 300 - 200 = 100
\(24.17+52.76+24.35\)
\(=24.\left(17+35\right)+52.76\)
\(=24.52+52.76\)
\(=52.\left(76+24\right)\)
\(=52.100\)
\(=5200\)
24 x 17 + 52 x 76 + 24 x 35
= 24 x ( 17 + 35 ) + 52 x 76
= 24 x 52 + 52 x 76
= 52 x ( 24 + 76 )
= 52 x 100
= 5200
~~~~~~~~~~Hok tốt~~~~~~~~~~
24 × 66 - 24 + 36 × 24
= 24 × (66 - 1 + 36)
= 24 × 101
= 24 × (100 + 1)
= 24 × 100 + 24
= 2400 + 24
= 2424
\(..=24x\left(66-1+36\right)=24.\left(65+35+1\right)=24.\left(100+1\right)=2400+24=2424\)